Subliminal perception Marcel (1983)



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Mental Reps Autumn Term 2001 Subliminal perception
Marcel (1983) Experiment Four
N=12 subjects , three masking conditions in separate sessions





RT (msec)

Unassoc’d

Associated

Facilitation

Unmasked control

590

528

+62

Pattern masked (dichoptic)

597

541

+56

Noise-masked (monoptic)

586

582

+4

Marcel (1983) Experiment Five






=> Consciousness does not equal activation

Cheesman & Merikle (1984, 1986)

In the Marcel experiments, if subjects not confident they definitely saw something, they may say “no” on every trial.


=> discrimination performance = 50%

But if subjects are forced to respond yes 50% of time, maybe they would be above chance?





  • Maybe Marcel had not found the objective threshold for discrimination?

Cheesman & Merikle presented subjects with one of four colour words (“red”, “green”, etc). On each trial, subjects had to say which word had been presented.


(Now even if subjects believed they saw nothing, have to guess something.)

After each block of 40 trials, the SOA was reduced until subjects were performing at chance.

After each block of trials, subjects estimated how accurate they had been.
- If they felt they had no information whatsoever, they were just guessing purely randomly, subjects gave an estimate of 25% correct (=chance expectation).


  • If they were certain, they would give an estimate of 100%.

- Subjects could give any value between 25% and 100%.




Subjective threshold = the SOA at which subjects believe they are performing at chance

Objective threshold = the SOA at which subjects really are performing at chance.

Results:




  1. The subjective threshold is reached at a higher SOA than the objective threshold.




  • the two thresholds are different



  1. Stroop priming is obtained for colour words presented below the subjective threshold, but NOT below the objective threshold.

Conclusion: BOTH results indicate unconscious processing below a subjective threshold.


But no evidence for unconscious processing below an objective threshold.
Research since then has confirmed it is easy to get unconscious perception below a subjective threshold, but very difficult below an objective threshold.
Greenwald (1992) found that 93% of the cognitive psychologists he surveyed regarded subliminal perception as having been demonstrated below a subjective threshold.

Is the subjective threshold just a curiosity or theoretically interesting?


Need to establish qualitative differences between knowledge above and below the subjective threshold.
Merikle & Joordens (1997)
Only two words used: Red/green.
“Red” or “green”

(variable SOA)

backward mask

&&&&& (in red or green ink)


Task: Name colour of ink.

On 75% of trials, the prime and target were incongruent (e.g. “red” followed by green ink)


And 25% of trials congruent

A conscious belief (e.g. “I am seeing the word RED”) can be combined with any other belief or desire to which it may be relevant in order to produce further beliefs or actions (in this case, to be prepared for green ink).


Unconscious knowledge cannot combine with just any other possibly relevant belief or desire to plan action.

=> Only conscious knowledge is inferentially promiscuous.

Marcel (1980)

Many hypotheses about the world are held unconsciously; one is selected for consciousness.


Procedure
Word 1 ---1.5s --> Word 2 ----1.5s--> Word 3

Lexical Unmasked Lexical

decision Pattern masked decision

Energy masked

Associative relation Examples

1. Congruent hand - palm - wrist

2. Incongruent tree - palm - wrist

3. Unassociated clock - race - wrist

+ other control conditions
Results:
Unmasked condition:

Congruent RT < Unassociated RT

Incongruent RT > Unassociated RT

-> facilitation only occurs for one meaning - the meaning related to prior context. Conscious processing is selective.


Pattern masked condition:

Congruent RT < Unassociated RT

Incongruent RT < Unassociated R

-> facilitation occurs for both meanings. Preconscious processing is nonselective.



Process dissociation applied to unconscious perception
Jacoby, Toth, Lindsay, & Debner (1992)
Procedure:
time event

1000 ms ' +'

500 ms 'glove'

50 or 500 ms 'patch' or 'staff'

500 ms 'flare'

500 ms


response pat--

Exclusion test: Do not use the presented words to complete the stem.
Inclusion test: Complete the stem with one of the words flashed or, if unable to do so, with the first word that comes to mind.

Results:

500ms 50ms Baseline

Exclusion .10 .50 .36

Inclusion .96 .63 .38


For 50 ms words:

Prob. of conscious perception = .13

Unconscious influence = .20

Momentary consciousness?
(See Allport, 1988, in Marcel and Bisiach, Eds, Consciousness in contemporary science)

Cumming (1971) D.Phil thesis Oxford


Sequential blanking
Series of letters presented at different locations on the screen.

Offset of one letter followed by onset of next.


Task: To search for “K”
4 1 2 3 5 <= order of appearance

R K L J T


--------------

blanked by lateral masking


fast “yes” followed by “oops – no”
O’ Brien (1972) D.Phil thesis Oxford

Which stimulus was pip synchronous with?


100%
which followed?

75%
which preceded?



50%



  • Instantaneous forgetting???

(consider this question again after last lecture in course)


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